String galvanometer



Jan. 2, 1934. F. o. HINDLE STRING GALVANOMETER a Shets-Sheet 1 FiledFeb. 27, 1935 Jan. 2, 1934. R Q HlNDLE A 1,942,027

STRING GALVANOMETER I Filed Feb. 27, 1933 3 Sheets-Sheet 2 Jan. 2, 1934.F o HiNDLE 1,942,027

STRING GALVANOMETER Filed Feb. 27, 1933 3 Sheets-Sheet 3 Patented Jan.2, 1934 UNETED STATES PATENT QFFICE STRING GALVANOMETER ApplicationFebruary 27, 1933. Serial No. 658,782

15 Claims.

This invention relates to new and useful im-' provements in stringgalvanometers, and has particular relation to improvements in the typeof instrument disclosed in my prior Patents Nos.

1,416,824. of May 23, 1922 and 1,702,650 of February 19, 1929, and isintended especially for use in the Electro-cardiograph, although it isnot limited to this use.

An object of the invention is to provide a string galvanometer includinga pole piece construction whereby the pole pieces are permanent- 1ysecured together against any relative movement.

Another object is to provide an improved meth- 0d of manufacturing andmounting the pole pieces for a string galvanometer.

A further object is to provide a string galvanometer including meansmounting the electro conductive string member and means so securing themounting means that it may be easily and quickly removed andanothersubstituted should a string break or should another string forany other reason be required.

A still further object is to provide an improved $5 construction wherebyit is not necessary to bore out the centers of the poles of the magnetsto receive the microscope tubes with the consequent reduction in fieldstrength.

An additional object is to provide a string gal-- vanometer of generallyimproved'construction including an improved base or mounting means andimproved. and simplified means for mounting the parts thereon.

Other objects and advantages will become ap- 85 parent from aconsideration of the following detailed description taken in connectionwith the accompanying drawings wherein a satisfactory embodiment of theinvention is shown. However, it will be understood that the invention isnot limited to the details disclosed but includes all such variationsand modifications as fall within the spirit of the invention and thescope of the appended claims.

In the drawings:

Fig. l is a front elevational view of the improved device, parts beingbroken away to show detaiis of construction;

Fig. 2 is a transverse vertical sectional view taken substantially alongthe line 2-2 of Fig. 1;

3 is a view partly in section and, partly in elevation, the view beingtaken substantially along the lines 3-3 of Fig. 1; t

Fig. l is a sectional View taken substantially along the line H of Fig.3;

Fig. 5 is a front elevational view of the base or mounting member alone;

Fig. 6 is a bottom plan view of the base with the magnet pole pieces inplace thereon;

Fig. '7 is a perspective View of the pole pieces; 30

Fig. 8 is a transverse sectional view illustrating a step in themanufacture of the pole pieces;

Fig. 9 is a sectional view through the completed pole pieces;

Fig. 10 is a view somewhat similar to Fig. 8 but a; showing a modifiedconstruction; and

Fig. 11 is a perspective view of a portion of a field magnet employed.

Referring in detail to the drawings, my improved instrument includes abase or mounting 79 means generally indicated at 12 and best shown inFigs. 5 and 6. This mounting member includes a plate-like portion 13preferably in the form of a casting of non-magnetic metal, as forexample aluminum. Integral with the plate 13 and extending nearly fromend to end thereof, at a point midway between its side edges, is araised portion or rib 14 slightly hollow or grooved in its upper surfaceto provide flanges 15 the purpose of which will later appear.Substantially centrally or in other location as desired the member 12 isprovided with an opening 16 for the passage of a screw or otherfastening means, and adjacent the respective ends of the rib 14 openingsor screw holes 17 are provided and the purpose of these openings willlater be fully set forth.

At diametrically opposite points on the side edges of the plate 13 andin parallel relation with the rib 14 and with one another a pair ofoutwardly extendingprojections or bearing members 18 and 19 are providedeach of said projections being hollow or formed with an openingtherethrough, the opening 20 in the outer portion of each projectionbeing of greater diameter than 95 the opening 21 in the inner portionthereof. Later in the description of the assembled device the functionsof these parts will be made clear. Strengthening ribs 22 are formed onthe inner surface of plate 13 and connect with the end portions of therib 14, and other strengthening ribs 23 are similarly formed on theplate 13 and connect the intermediate portion of the raised portion orrib 14 with the projections or bearing members 18 and 19.

According to the present invention pole pieces 24 and 25 are soconstructed and connected as to form substantially a solid-unit whereinthe said pole pieces can have absolutely no relative moven permanentlyconnected.

ment. To attain the most efiicient Way of causing the magnetic flux toconcentrate at the center it is well known that these pole pieces shouldbe substantially wedge shaped in transverse section and should bearranged with their narrow edges in opposed relationship. Inmanufacturing the pole pieces I .take a .cross sectionally square orrectangular bar 526 isee Fig. of {magnetic ,rnaterial as iron and millor cut away a portion thereof to provide a ll-shaped groove 27 the angleof the side walls of which may be anything desired but usually isapproximately 45. The apex of this groove is located slightly toone-side-of the center or the bar 26.

Next, according to one anathodgl welding-ether the two walls of thegrooye by depositing welding material (non-mag n etic metal such asbronze) 28 in said groove until it is entirely or substantially entirelyfilled as best shownin 9. The magnetic bar 26 is first heated to a pointthat as the metal :28 :is melted and-deposited it adheres firmly to theiron landtller-mS aibodyiused to and dcrnring .a weld laetiween 11118;Side Walls the groove127-whereby said avails are inieaidlyand 'ilhisprocess is (continued ezntil the groove is dill-led with :the henm neticmetal isnbstantial y in e ral si'iiuctnre provided. ":llhereafiter, (seeFig. 19) a similar groove 29 is formed in the @pposite :Side of said barof metal an a :the cornpletion of she groove a saw or tether .slot :39is provided separating :the remain n 19 215 0135. the bar into the polepieces i261 Iwd 125.. This .slot 30 may extend slightly into -:thenon-magneti 1 metal 28 and is of a width to properly space the said polepieces.

Another method of this p le member is to clap. L t. e two triangularpole pieces 24 and 25 in then proper relative positions in a snitalblsupport then fill in .the groove at one side with the nonrma-gnetic Weldmetal 128 as de scribed.

As an alternative method .(see Fig. 10) after the groove 2'] is formed,.or the two triangular pole pieces clamped proper itelation, New

31 of non-magnetic metal. as for example brass, bronze, or the like, maybe secured or arsed in position filling the groeve, as by brazing, thehard connecting brass er solder bemg at 32. According to this method thesolid her would then be grooved inits opposite serface sawed orotherwise cut through ts sepa rzate ts remaining portions into polepieces the proper distance apart. In each instance the magnetic polepieces are 59 connected as t form a iitary strucyure in which these polepieces weuld ibe incest-isle of rela ive m vemen as they are weldedtogether.

Th H arr po piece stru ture made as above set icrth may no b pro ided ih tanned recesses 33 arrange one in the outer race or each pole djacenteach end the eof.- A so aligned. ne. h s 34: a e pr ided in he polepieces th c nter of he e la open ngs be ns i nm nt w t the ce te of thslo o space 3.0 tor-med between the pol pie es s abo e d scribed. Itwill e ppa ent th t t e ta o en inss 33 and if des r d the aligned 9 erii s 3e d 5 a be provid d n t e ba 26 e p e uch bar is treated to formthe pole pieces.

The pole piece unit constructed as above described is arranged on therib 14 with its nonmagnetic body portion 2-8 disposed against the outersurface of said rib and the unit is of such width as to fit snuglybetween the flanges -15 of the rib whereby the unit is held againstlateral movement. A screw 36 is then passed through the opening 16 inplate 13 and threaded into a tapped opening 37 in the portion 28 of thepole piece unit, or additional screws may be provided, whereby said unitis drawn tightly against the face tof :the rib i114 and held againstmovement outwardly of the flanges 15 of said rib. From this it will beseen that the unit is easily mounted and is firmly held against anymovement relaitive to plate or base 13.

Pairs pf coils 38 and 39 are arranged at the respective ends or adjacentthe respective ends (Of the ;pole pieces and one coil of each pair isarranged at the router side of the pole piece 24 "Whil .the :remainingcoils are arranged at the outer side .of the polepiece 25. The coilsenclose cores 40 through which extend screws or bolts 41 having theirinner ends threaded into the tapped openings 33 before referred to. Asubstantially 1U.- shaped or horseshoe 'fie'ld piece 42 is arranged :ateach end of the device 'or instrument :and adjacent :the free end ofeach of its arms :each of said field 21116088 is provided with an(opening through which the screws 41 extend whereby said field :piecesare mounted with their ends in close relation .to the :cores and. withthe cores clamped between said ends and the :pole :pieces. with thisarrangement any stress or strain resulting from the strong :mag- 13netic (fierce present when :the machine is operating will inotlbesequined to be :taken up by the parts 42 and their connections and willnot result in any relative movement between the pole pieces 24 and 25,.

Improved means are provided for supporting an electric conductive stringmember 43 in the space '30 between the oppcsed pole pieces 24 and 25.This means as here show-n includes an-elonliLG gated block or strip 44of insulating material as 1555 for example bakel-ite or the like. At itsinner side and between its ends the strip 44 carries an elongated block45 to the rapper end of which is secured an insulating block '46 havinga metal contact member 47 thereon and to which is se- 129 cured one endof the string 43.

Adiiaeent its lower end the block 45 is provided with a slot snuglyreceiving the outer end portion of a flat spring member 43, the inner orprojecting end-0f is loaded-or strengthened -5 lon arm is provided withan opening throu h hich passe the inner of a Screw 52 whereby the isheld a ainst lat ral mov m n As indicated above as the free portion ofspring 48 is short this lateral movement of arm 51 is also practicallyprevented independently of screw 53 This insures the conductor string 43will not be throvwn laterally or out of center when its tensi n- 1 adjuted.

The lower end or string member 43 is secured 9 1. 5. 0 a m 5.0 of the L.shaped and 149 passing through the strip 4e and the block 45 is a screw53 the inner end of which. engages the upper end portion of arm 51. Thisscrew 53 includes an operating head 54 at the outer side of mountingstrip 44 and it will be understood 150 that by adjusting this screw thelong arm of the L-shaped member may be pressed inwardly to rock saidmember by flexing the spring 48 whereby the short arm of the member willbe moved downwardly. This, of course, will result in increasing thetension of the string member 43.

A plate (see Fig. 3) is secured to the outer side of each of the polepieces 24 and 25 as by screws 56, and at their inner edges these platesabut the outer edges of the flanges 15, and at their outer edges theseplates fit into grooves provided for that purpose in the supportingstrip 44. These plates serve to assist in properly positioning thesupporting means for the string member whereby to locate said stringmember in the space 30 between the opposing faces of the pole pieces.Additionally, a leg or arm member 57 is secured to the inner side of thestrip 44 adjacent each of its ends, and these arm members are of a widthto snugly fit between the flanges 15 on the rib 14 and are of suchlength that when they engage the upper surface of said rib 14 the partsare so arranged that the string member 43 is properly located within thespace between the pole pieces.

The strip 44 and the parts carried thereby; form the support for theelectro conductive string member 43, and to secure this support in placescrews 59 are passed through the openings 17 in the base, and at theirinner or forward ends are threaded into the said strip as best shown inFig. 2. Obviously, should the string member break, the screws 59 may beretracted and the entire support for the string member lifted from thedevice. A second support having a string member properly mounted thereonmay then be readily applied and secured in place by a tightening of thescrews 59. The string members may be properly located on the supports atthe factory and one or more extra supports kept on hand by the user whomay then readily replace a support should its string break or should itbe desired to replace it for any other reason. No skill is required inmounting or dismounting a support from the device, and therefore muchtime and trouble is saved by the user over the old devices where if astring conductor broke a new one had to be mounted and centered, whichwas a very delicate and long tedious operation.

Extending through the projection or bearing 18 and centered therein asby screws 60 is a microscope 61. The inner end portion of thismicroscope is arranged in the opening 35 in the pole piece 24 and themicroscope is focused on the string member 43. A second microscope 62 ismounted in the bearing member 19 and is' centered therein as by thescrews 63. This microscope 62 has its inner end portion located in theopening 34 through the pole piece 25 and is also focused on the stringmember 43. It will be noted that with the arrangement of the pole piecesand the coils and their cores as above described and illustrated it isnot necessary to bore out the magnets to receive the microscope withconsequent reduction in field strength, but there is required only asmall hole 34 or 35 in the center of the magnet pole pieces to admit themicroscopes. In the use of the machine a bright white light is focussedon the string by one microscope, as for example the microscope 61, andthe shadow cast by the string member is picked by the second microscopeand enlarged and passed to any suitable camera means, not shown,operating with a sensitized strip. The use of the ma: chine in makingcharts is fully understood and fully disclosed in the prior art and afurther description thereof is believed unnecessary. The leads from asuitable source of exciting current and the leads for the current to bemeasured or recorded are connected to the magnet coils and the, stringconductor respectively in the usuall manner.

From the foregoing description taken irr connection with the drawings itwill be appreciated that I have provided a. string galvanometer of asimplified construction. Further, it will be noted. that the device isnot of the usual extremely heavy constructionheretofore employed for thepurpose" of holding the magnet pole pieces against relative movement. Bythe method disclosed the pole pieces are so secured together as to forma rigid strong unit whereinrelative movement between the pole pieces isimpossible. With thepresent construction the parts are few and easilyassembled and in the event of the breakage of a string member the entirestring support may be easily and. quickly removed and another supportand string substituted.

Heretofore, heavy constructions have beenemployed in devices of thiskind. In the present device the field pieces 42 are not secured directly1,90: to the plate or support 13 and are held in placesolely by thescrews 41. Further, the ends of these pieces 42 do not abut the edges ofthe projections l8 and 19 but are spaced slightly there from wherebymovement resulting from the application of current to the coils ispermitted by the field pieces without displacing the pole pieces or thestring conductor. 1

It will thus be evident that with my improved construction the polefaces are held rigid in per- 11; feet alignment with the microscopes.The pole faces are also held a certain fixed distance apart and they maybe placed close together to secure maximum magnetic flux. It hasheretofore been impossible to economically construct a means of 11;;holding the magnetic pole pieces immovable due to the tremendousattraction of the two pole pieces when under the magnetic strain. Thiswas a serious difficulty as any movement of the pole pieces or theirfaces will cause misalignment 12a of the microscopes or the stringconductor. The shifting of either of these component parts causesdifficulties in using the instrument. These difficulties are effectivelyovercome in my improved device as the pole pieces are in efiect integralwith each other and are mounted on the non-magnetic metal frame, themicroscopes are mounted on the same frame and the mag-, netic cores forthe coils, and the connecting field pieces are attached to the polefaces only. 13-3 Therefore any distortion or magnetic striction isabsorbed by the yielding of the field pieces.

Having thus set forth the nature of my invention, what I claim is:

l. Ina galvanometer, a pair of pole pieces of magnetic material wedgeshaped in cross section arranged with a pair of their narrower edges in;opposed spaced relation, and non-magnetic metal filling the spacebetween a pair of side walls of said pieces and fused to these Walls toprovide a unitary structure.

2. In a galvanometer, an electro magnet having opposed spaced polepieces, an electro conductive string member, means supporting saidmember with the member disposed in the space between said opposed polepieces, each of said pole pieces wedge-shaped in transverse section andsaid pole pieces disposed with their narrower portions in opposedrelation, means holding said pole pieces against relative movement, andsaid i;"

' ass-1r or a posed slightly's'paced pole" pieces} each of said polepieces wedge shaped in transverse section and pure ieces stressed withtheir narrower edges dpposisgreiatien, h'o'i'cl ing said r al-alepiecesagainst relative movement arid sulistan'tialh' filling the space themat" their under oes said means disguising: a; body' of non-magnetic;material" fused tosaid pore pieces wuerety" to form; them into at saidunit disposed iii and saugl yntting between the: wens or tire g' rodve'base mews engaging said andhoidii'ig roove, an electro' conductivestring member; creams supportirig' saidstr'ing member in the spacebetween said we pieces.

i. in a gaivanoxneter; ereetremagnet com prising opposed spaced 15616pieces, each 6t pole pieces wedge shaped in transverse": section andsaid pol pieces Witl'i their narrow r edges in opposing relation, meansholding psie rees against relative movement sobsti'ai-itiail'yfillingthe space Between them at their urid'ef'side's; and said; means;comprising a body of nos-magnetic mati ial idsed t6) eachor said polepieces whereby: to miss them into a v 5. The iiithd of a rigid unitim1ad-- iiig a pair of tr ansv'ersergr wedge shaped po'l piecesaffaiigdiii s aces relationship with; their narrower edges in opposes relation,the same comprising" pfvidifig a or magnetic mittens},- fdfriiiiig av-greove one side or said bar, fill ing s'aidgrooi e with nonmagneticmetal fused t6 tirewant of tne groove, forming: a simi- Iar' gi'odve theopposite side at said and their cutting through the remaining portion ofthe at the apex: of said second grdove.

6. method orienting a rigid unit mama: mg a 6! transversely Wedge shapesopposed pole pieces arranged inspaced r'ilatidrisliip with their saris iedges he opposed reiatiori, the same comprising providing a car ormagnetic metal, forming a v groov' one side or said bar, filling saidgroove with non-ma netic ifit'al deposits ing molten non-magneticIfitaltherein whereby t6 weld together the walls of said groove, remi mga similar groove in the opposite side or said bar, and then cuttingthrough the remaining portion of the bar at the apex of said secondroove.-

'7; The frithod of forming a rigid unit memomg a pair of transverselywdg' shaped opposed pole pieces arranged iii spaced relationship withtheir narrower edges in opposed relation, the same comprising providinga liar of inagfietic metal, forming a V-groove in one side of said bar,filling said groove by brazing to the walls thereof a wedge shaped blockor non-magnetic metal, forming a similar groove in the opposite side orsaid bar, and then cutting through the remaining portion of the bar atthe apex of said second groove. I

8. In a galvanometer, a base or mounting member, said member comprisinga plate-like portion of non-magnetic inetal, a centrally located raisedportion on said plate, a pair of outwardly directed parallel projectionson said piste and a1- iari'ged at diametrically opposite points thereonand at the sides of said raised portion, opposed slightly spaced polepieces mounted on said raised portion, a pair of coils at each fid ofsaid plate and arranges one at each side of and closely adjacent saidpole pieces, a substantially U shaped field piece at each end of saidplate and each hearingits respective endsdisposed at the outer'endoi oneof said pairs of coils, a bar passing through each of said coils andmounting the same, said bars having their outer ends secured.

tdthe adjacent ends 0t said field pieces and having their inner endssecured to one of said pole pieces, an electro conductive string member,means supporting said member to dispose it between said pole pieces,aligned openings through said pole pieces, a telescope mounted in eachof said projections, and said telescopes focussed on said string memberthrough the openings in the pole piecest 91- In a ga lv'anornetei",- amounting member, said member including a plate-like" portion ofnonmagnetic metal, opposed spaced pole pieces mounted on said plate, apair of coils adjacent each end or said pole pieces, said coils at therespsctive ends of-' the pole pieces arrangedv one can at the outer sideof and closely adjacent each of said pole pieces, a substantiallyiii-shaped field piece" arranged toward each end of said plate, saidfield pieces at the respectiveends of the plate having their endsdisposed at the outer ends of coils adjacent the respective ends of theplate, a bar connected to each of said field piece ends and passingthrough the adjacent coil and into the adjacent pole piece whereby tomount the field pieces and coils, an electro conductive string member,and means supporting said member to dispose it in the space between saidpole pieces.

10.- In a galvanometer, a mounting member, a pair of parallel spacedflanges on said member and forming a groove, a pair of opposed spacedpole pieces on said member, a support, an electro- Gonductiv'e stringmember mounted on said support, a pair of arms on said support andadapted to enter said groove and engage the bottom thereof to disposesaid string member in the space between said pole pieces, and means tosecure said support to said mounting member with said arms in saidgroove and engaging the bottom thereof.

11. In a galvanom'eter', a mounting member, a pair of parallel spacedflanges on said member and forming a groove, a pair of opposed spacedpole pieces on said member, a support, an electro conductive stringmember mounted on said support, a pair of arms on said support adaptedto enter said groove and engage the bottom thereof to dispose saidstring member in the space between said pole pieces, and screws passingthrough said mounting member and into said support and securing saidsupport to the mounting if member with the ends of said arms drawntightly into engagement with the bottom of said groove.

12. In a g'alvanometer, a mounting member, a pair of opposed spaced polepieces on said memher, a support, an electro conductive string memi ber,means mounting said string member on said support, said means disposedat the inner side of said support and including an L-shape-cl member, ashort flat spring having the short arm of said L-shaped member rigidlysecured thereto, said u string member having one end secured to theshort arm of said L -shape'd member, means engaging the other arm ofsaid L-shaped member and adjustable to rock it by flexing said spring totension said string member, and means to secure said i.

support to said mounting member with said string member disposed in thespace between said pole pieces.

13. In a galvanorneter, a mounting member, a pair of parallel spacedflanges on said member and forming a groove, a pair of opposed spacedpole pieces on said member, a support, an electro conductive stringmember, means mounting said string member on said support, said meansdisposed at the inner side of said support and including an L-shapedmember, a short flat spring having the short arm of said L-shaped memberrigidly secured thereto, said string member having one end secured tothe short arm of said L-shaped member, means engaging the other arm ofsaid L-shaped member and adjustable to rock it by flexing said spring totension said string member, a pair of arms on said support and adaptedto enter said groove and engage the bottom thereof to dispose saidstring member in the space between said pole pieces, and means to securesaid support to said mounting member with said arms in said groove andengaging the bottom thereof.

i l. In a galvanometer, a mounting member, a pair of opposed spaced polepieces on said member, a support, an electro conductive string member,means mounting said string member on said support, said means disposedat the inner sidev of said support and including an L-shaped member, ashort flat spring having the short arm of said L-shaped member rigidlysecured thereto, said string member having one end secured to the shortarm of said L-shaped member, means engaging the other arm of saidL-shaped mem ber and adjustable to rock it by flexing said springwhereby to tension said string member, said means including a screwextending through said support and operable from the outer side thereof,and means to secure said support to said mounting member with saidstring member disposed in the space between said pole pieces.

15. In a galvanometer, a mounting member, said member comprising aplate-like portion of non-magnetic metal, a centrally located raisedportion on said plate, said raised portion grooved in its outer surfaceto provide a pair of parallel flanges, a unit comprising a pair ofopposed spaced transversely wedge-shaped pole pieces connected at theirundersides by a body of nonmagnetic metal fused to them, said unitdisposed on said raised portion of the mounting member and snuglyfitting between the walls of the groove thereof, a screw passing throughsaid mounting member and into said body of non-magnetic material andserving to draw said unit tight against the bottom of said groove, fieldmagnets associated with said pole pieces, an electro conductive stringmember, and means supporting said string member in the space betweensaid pole pieces.

FREDERIC O. HINDLE.

